1. Field of the Invention
The invention is directed to a network and in particular to an architecture for high-speed optical mesh networks.
2. Background Art
Network users and providers are looking for reliable networks at acceptable bandwidth (BW) cost. Reliability is the ability of the network to carry the information from source to destination with errors below a certain threshold.
Protection is a traffic preserving strategy for managing the usage of the working and the dedicated protection (redundant) bandwidth in the network. Automatic protection acts quickly enough to ensure that the client's connections remain unaffected by failures. SONET/SDH (synchronous optical network/ synchronous digital hierarchy) is provided with very effective and fast protection mechanisms, which make this technology a strong contender for the networks of the future.
SONET/SDH is a physical carrier technology for optical transmission, which can provide transport for services such as IP, ATM, Ethernet, SMDS, frame relay, DS-n, T1, E1, etc. The SONET/SDH standards define the physical interface, optical line rates known as optical carrier (OC) signals, a frame format, and an OAM&P protocol. The user signals are converted into a standard electrical format called the synchronous transport signal (STS). The optical carrier OC signals are named after the STS they carry. For example, and OC-3 carries an STS-3.
SONET/SDH protection protocols are designed for various network configurations, such as linear networks (1+1; 1:1 and 1:N protection schemes) and ring networks (unidirectional path switched rings UPSR and bidirectional line switched rings BLSR). As well known, the two digits used to define the type of protection refer to the number of “protection” (spare) fibers and the “working” fibers for a certain span. 1+1, UPSR and 1:1 schemes require 100% redundancy. 1:N, 2F (two-fiber)-BLSR and 4F-BLSR schemes require less than 100% network overbuild, as extra traffic (traffic of lower priority) may be carried between nodes on the protection bandwidth/fibers during normal operation conditions. The extra traffic is however lost when a protection switch occurs.
Typically, protection switching times are less than 50 ms for SONET. On the other hand, protection implies reserving bandwidth, and therefore transport networks are often 100% overbuilt.
SONET rings are currently the topology of choice in fiber deployment. The prime motivator for rings versus linear transport is higher survivability. A ring protects against simultaneous failure of the protection and working fibers and saves intra-ring and inter-ring pass-through traffic during node failure/isolation. In addition, while the traffic physically travels from node to node in a ring configuration, the services are practically connected in a mesh network, where each node exchanges services with any other node of the network.
The UPSRs are currently used in access networks and therefore they are not discussed herein.
The BLSR are extensively used in the backbone networks and therefore they are built for higher rates such as OC-48, OC-192, etc. Protection switching is done at the SONET line (multiplex section) sublayer. As indicated above, without extra traffic, 50% of the bandwidth available is used to protect against line or node failure conditions, i.e. 50% of the ring BW is used for the ‘working traffic’ and 50% for the ‘protection traffic’. This means that network owners must sell the protection bandwidth at a cheaper rate than the protected or working bandwidth price. Often the protection bandwidth sits completely unused and is therefore unavailable to produce income.
WDM (wavelength division multiplexing), dense WDM (DWDM) and the technical advances in the optical switching technologies resulted in an evolution of the transport network from ring to mesh configurations. Clearly, the most economical strategy for such an evolution is to adapt the existing BLSR's to mesh architectures, for preserving the huge HW and SW investment in the existing networks. However, current protection switching protocols are specifically designed for rings and are not readily applicable to mesh transport networks.